Busways for electrical distribution systems are commonly understood in the art to include multiple pre-assembled sections of a duct containing individually insulated, usually flat electrical conductors or busbars. The individual sections are designed to be easily connected, both electrically and mechanically, end-to-end to form any desired length. In a plug-in busway, at least some of the sections are equipped with built-in electrical receptacles adapted to receive plug-in units containing electrical equipment to be connected to the busway, such as circuit breakers and different kinds of switches and control devices. To ensure the integrity of the electrical connections between the plug-in units and the busway, and to protect the plug-in units, restraint devices are typically provided on the plug-in units to mechanically connect or fasten the plug-in units to the busway.
In many applications of plug-in electrical busways, there has been an increasing need to accommodate a high density of plug-in units along portions of the busways. Many plug-in units require working access between adjacent plug-in units because the mechanisms for attaching the plug-in units to the busway are located on the exterior surfaces of the side walls of the units and require access for manual adjustments during the installation process. These attachment mechanisms increase the overall envelope size of each plug-in unit, which in turn reduces the allowable density of plug-in units on the busway.